Composite solid electrolytes for rechargeable energy storage devices

ABSTRACT

A device includes an ion-conducting membrane with ion-conducting ceramic particles, and an ion-conducting polymer that surrounds the ion-conducting membrane. The ion-conducting polymer includes a pressure-deformable film with a glass transition temperature lower than an operation temperature of the device.

BACKGROUND

Energy storage devices such as lithium ion batteries have high energydensity, and provide a compact, rechargeable energy source suitable foruse in portable electronics, electric transportation, and renewableenergy storage.

Liquid electrolytes used in Li-ion batteries can reduce battery cyclinglife, and solid electrolytes can be used to provide safer and longerlasting batteries. Suitable solid electrolyte materials should have aunique combination of characteristics such as, for example, high Li-ionconductivity, high elastic modulus, electrochemical stability, and goodinterfacial contact with battery electrodes.

SUMMARY

In various embodiments, the present disclosure is directed to asolid-state electrolyte for an energy storage device that includes highion conductance, can be made thin and flexible, and can suppressdendrite growth and penetration into the electrolyte at the surface of ametallic electrode.

In one aspect, the present disclosure is directed to a device includingan ion-conducting membrane and an ion-conducting polymer that surroundsthe ion-conducting membrane.

In another aspect, the present disclosure is directed to a deviceincluding an ion-conducting membrane including ceramic particles, and afilm surrounding the ion-conducting membrane including an ion-conductingpolymer, wherein the ion-conducting polymer is pressure-deformable andhas a glass transition temperature lower than the device operationtemperature.

In yet another aspect, the present disclosure is directed to a methodfor making an energy storage device including dipping an ion-conductingmembrane into a pre-polymer mixture of an ion-conducting polymer,wherein the pre-polymer mixture includes polymerizable compounds, anLi-ion salt, a polymerization initiator, and an optional ionic liquid.The method further comprises polymerizing the pre-polymer mixture undercuring conditions (for example, UV or visible light, heat, microwaves,and combinations thereof) when it is on the ion-conducting membrane. Themethod may further include assembling the resulting free-standing solidelectrolyte with electrodes.

In yet another aspect, the present disclosure is directed to a methodfor making an energy storage device including dipping an ion-conductingmembrane into a pre-polymer mixture of an ion-conducting polymer,wherein the pre-polymer mixture includes polymerizable compounds, anLi-ion salt, a polymerization initiator, and an optional ionic liquid.The method also includes assembling the ion-conducting membrane, whileit is still wet from the pre-polymer mixture, with electrodes to form astorage device. The method further includes polymerizing, in-situ, thepre-polymer mixture inside the storage device by applying stimuli (forexample, heat).

The solid-state electrolyte of the present disclosure may providebenefits in a rechargeable lithium battery including, but not limitedto: (1) improved interfacial contact with solid electrodes which canresult in low area specific resistance (ASR) toward Li-ion transportacross an Li-conducting membrane (surface planarization effect); (2)improved accommodation of electrode volume changes (cushion effect); and(3) improved interfacial stability toward Li-electrodes (protectioneffect). The all solid-state Li-battery electrolyte provides both theimproved performance of a solid electrolyte along with the increasedenergy density provided by use of a metallic Li-anode, withoutcompromising safety or compactness.

The details of one or more embodiments of the present disclosure are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the present disclosure will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic, cross-sectional view of an ion-conductingmembrane that may be incorporated into a solid electrolyte.

FIG. 2 is a schematic, cross-sectional view of an energy storage deviceincluding the ion-conducting membrane of FIG. 1.

FIG. 3 is a schematic, cross-sectional view of a solid electrolyte thatmay be incorporated into an energy storage device such as a Li-ionbattery.

FIG. 4 is a schematic, cross-sectional view of an apparatus suitable forforming a solid electrolyte.

FIG. 5 is a flow diagram illustrating an example technique for formingan example Li-ion battery.

FIG. 6 is a flow diagram illustrating an example technique for formingan example Li-ion battery.

FIGS. 7A-7B are overhead plan views and cross-sectional SEM images ofthe ion-conducting membrane of Example 1.

FIG. 8 is a cross-sectional SEM image of the solid-state electrolyte ofExample 4.

FIG. 9 is a plot of the plating and striping profile of the cell ofExample 6.

FIG. 10 is a plot of the charge-discharge (plating and stripping)profile of the cell of Example 9.

FIG. 11 is a plot of the galvanostatic cycling behavior of a Li/Lisymmetric cell assembled with the crosslinked PEG ion-conducting polymerelectrolyte as described in Comparative Example 1.

FIG. 12 is a plot of the galvanostatic cycling behavior of a Li/Lisymmetric cell assembled with only the crosslinked POSS-PEGion-conducting polymer electrolyte as described in Comparative Example2.

Like symbols in the figures indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of an ion-conducting membrane 100including ion-conducting ceramic particles 114 and an insulatingpolymeric binder 112. The ion-conducting membrane 100 includes a firstmajor surface 124 and an opposing, second major surface 126. In someembodiments, the ion conducting membrane 100 includes a contiguous solidstructure of fused or sintered ion-conducting ceramic particles 114. Inother embodiments, the ion-conducting ceramic particles 114 may belinked by an optional insulating polymeric binder 112, wherein at leasta portion of the ion-conducting ceramic particles 114 extend from thefirst surface 124 to the second surface 126. In some embodiments, theion-conducting ceramic particles 114 in the ion conducting membrane 100form a single layer. In various embodiments, which are not intended tobe limiting, the thickness of the ion-conducting membrane 100 is about0.1 microns to about 100 microns.

The insulating polymeric binder 112 may be chosen from, for example,cyclo-olefin polymers, poly-para-xylylenes, benzocyclobutenes, olefinaddition polymers, olefin addition copolymers, ring opening metathesispolymers and reduced forms thereof, fluorocarbon addition polymers,fluoroether polymers, cyclobutyl fluoroethers, polyarylenes, polyaryleneethers, polybenzoazoles, polysiloxanes, silsequioxanes,polycarvosilanes, and combinations thereof. In some embodiments, thepolymeric binder is selected such that the ion-conducting membrane 100is flexible.

In various embodiments, the ion-conducting ceramic particles 114 have anelastic modulus of greater than about 6 GPa. In some embodiments, ashear modulus greater than 6 GPa may suppress dendrite formation on thesurface of a metallic electrode and prevent dendrite penetration intothe ion-conducting membrane 100. More specifically, a shear modulusgreater than double the shear modulus of Li, wherein the shear modulusof Li is 3.4 GPa, may efficiently suppress dendrite growth. Theion-conducting ceramic particles 114 may be chosen from, for example,LiPON, LISICON (Li₁₄Zn(GeO₄)₄), LAGP (Li_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃),LATP (Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃), LATTP(Li_(1.6)Al_(0.5)Ti_(0.95)Ta_(0.5)(PO₄)₃), LLZO (Li₇La₃Zr₂O₁₂), dopedLi₃N, Li₂S—SiS₂—Li₃PO₄, Li₇P₃S₁₁, Li₁₀GeP₂S₁₂ and mixtures andcombinations thereof.

FIG. 2 illustrates an energy storage article 200 including a solid-stateelectrolyte 222. The solid-state electrolyte 222 includes anion-conducting membrane 220 (as shown in FIG. 1) surrounded by anion-conducting polymer 210. The solid-state electrolyte 222 has a firstsurface 206 and a second surface 208, and in some embodiments, the firstsurface 206 and the second surface 208 are substantially planar. Theenergy storage article 200 further includes a first solid electrode 202and a second solid electrode 204. In the embodiment shown in FIG. 2, thefirst solid electrode 202 directly contacts the first surface 206 of thesolid-state electrolyte 222, and the second solid electrode 204 directlycontacts the second surface 208 of the solid-state electrolyte 222, butdirect interfacial contact is not required. In some embodiments, whichare not intended to be limiting, the first solid electrode 202 is ananode, and the second solid electrode 204 is a cathode.

Suitable first solid electrodes 202 may be chosen from Li-intercalatinggraphitic anodes, lithium titanate (LTO), silicon, metallic Li-anodes,and the like. In some embodiments, metallic Li-anodes may provide aspecific anode capacity almost 10 times larger than that of anLi-intercalating graphitic anode, and metallic Li-anodes may furthermaximize the overall energy density of the energy storage device 200.

In various embodiments, the average distance between the first solidelectrode 202 and the ion-conducting membrane 220 may be less than about10 microns, or less than about 5 microns, or less than about 1 micron,or less than about 0.2 micron. In some embodiments, the average distancebetween the second solid electrode 204 and the ion-conducting membrane220 may also be less than about 10 microns, or less than about 5microns, or less than about 1 micron, or less than about 0.2 micron.

In some embodiments, the ion-conducting polymer 210 may improve theinterfacial contact with one or both of the solid electrodes 202, 204.If the solid-state electrolyte 222 formed by surrounding theion-conducting membrane 220 with the ion-conducting polymer 210 includesa substantially planar first surface 206 or a planar second surface 208,surface planarization effects can improve interfacial contact with thesolid electrodes 202, 204. Surface planarization effects may also resultin low area specific resistance toward Li-ion transport across aLi-conducting membrane.

Because the ion-conducting polymer 210 is thin, even if theion-conducting polymer has lower conductance than the ion-conductingmembrane 220, there can still be good ion conductance across solid-stateelectrolyte 222.

In some embodiments, the ion-conducting polymer 210 may be selected frompressure deformable materials, which may accommodate volume changes thatmay occur in the energy storage device 200. For example, volume changesmay occur during charge or discharge cycles in either or bothelectrodes, or may occur during various applications of the energystorage device 200. For example, a Li-ion battery including asolid-state electrolyte of the present disclosure may be used as arechargeable battery for a cell phone. If a user of the cell phone wereto sit down with the cell phone in his or her pants pocket, the volumeof the Li-ion battery could change upon the increase in pressure on thecell phone. A pressure deformable ion-conducting polymer 210 may allowfor volume changes to the solid-state electrolyte 222 without causingdamage to the storage device or the ion-conducting membrane 220, whichis referred to herein as a cushioning effect.

The ion-conducting polymer 210 in a solid-state electrolyte 222 may alsoallow metallic Li-electrodes or the like to be used in an energy storagedevice in place of Li-intercalating graphitic electrodes. In someembodiments, the ion-conducting polymer 210 may be selected frommaterials that are electrochemically stable when in contact with ametallic electrode, whereas the ion-conducting membrane 220 (morespecifically ion-conducting ceramic particles in the ion-conductingmembrane 220) may be selected from materials that are notelectrochemically stable with metallic electrodes. As used herein,electrochemically stable refers to a material that will notsubstantially react when placed in contact with a metallic electrodematerial.

Materials that are electrochemically unstable with metallic electrodesmay have a higher conductance than those that are stable with metallicelectrodes. Therefore, an electrochemically unstable material for theion-conducting membrane 220 may provide the solid-state electrolyte 222with a desired conductance, while an electrochemically stableion-conducting polymer 210 surrounding the ion-conducting membrane 220can make possible the use of metallic electrodes in contact with thesolid-state electrolyte 222.

FIG. 3 illustrates an example of a solid-state electrolyte 300 includingan ion-conducting membrane 320 (as shown in FIG. 1) surrounded by anion-conducting polymer 310. In various embodiments, the ion-conductingpolymer 310 may be chosen from linear polymers, crosslinked polymers,star polymers, and block copolymers. In some embodiments, which are notintended to be limiting, the ion-conducting polymer 310 may have a glasstransition temperature (T_(g)) lower than the device operationtemperature.

In some embodiments, the ion-conducting polymer 310 may include acompound that releases Li-ions, such as a Li-salt. Suitable Li-saltsinclude, but are not limited to, lithium hexafluoroarsenate (LiAsF₆),lithium perchlorate (LiClO₄ ⁻), lithium hexafluorophosphate (LiPF₆),lithium tetrafluoroborate (LiBF₄), lithium trifluoromethanesulfonate(LiCF₃SO₃), lithium nitrate and lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI).

In some embodiments, the ion-conducting polymer 310 may include an ionicliquid, which as used in this application refers to an ionic, salt-likematerial that is liquid below a temperature of about 100° C. and has amelting point below room temperature, or below about 20° C., or belowabout 0° C. Suitable ionic liquids include, but are not limited to,1-methyl-1-propyl piperidinium bis(trifluoromethylsulfonyl)imide,1-butyl-1-methyl piperidinium bis(trifluoromethylsulfonyl)imide,1-ethyl-1-methylpyrrolidinium tetrafluoroborate,1-methyl-1-propylpyrrolidinium tetrafluoroborate,1-butyl-1-methylpyrrolidinium tetrafluoroborate,1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide,1-methyl-1-propylpyrrolidinium bis(trifluoromethyl sulfonyl)imide,1-butyl-1-methylpropylpyrrolidinium bis(trifluoromethylsulfonyl)imide,1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide,1-methyl-3-propylimidazolium-bis(trifluoromethylsulfonyl)imide,1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide,1-ethyl-3-methylimidazolium-tetrafluoroborate,1-methyl-3-propyllimidazolium-tetrafluoroborate,1-butyl-3-methylimidazolium-tetrafluoroborate, and1-propyl-3-methylpyridinium-bis(trifluoromethylsulfonyl)imide.

In some embodiments, the ion-conducting polymer 310 may include anoptional inorganic filler. In some embodiments, the inorganic filler mayhelp reinforce the ion-conducting polymer 310, which may be soft. Insome embodiments, the inorganic filler may also enhance the shearmodulus of the ion-conducting polymer 310. In some embodiments, theinorganic filler acts as a reinforcing filler and has multiple sitesavailable for crosslinking. Suitable inorganic fillers may be chosenfrom, but are not limited to, carbon nanotubes, silica nanoparticles,POSS compounds, metal oxides, and combinations thereof.

POSS compounds of the present disclosure are molecular-sizednanoparticles having an arrangement of atoms or molecules bonded tocreate a fully or a substantially bounded space. In some embodiments,which are not intended to be limiting, the term POSS compound refers toresins having the structures (I), (II), or (III) below, where:

is denoted by the formula T₈ ^(R), where T represents RSiO_(3/2);

is denoted by the formula T₁₀ ^(R), where T represents RSiO_(3/2); or

is denoted by the formula T₁₂ ^(R), where T represents RSiO_(3/2).

In each of the structures (I)-(III) above, R is independently selectedfrom polymerizable groups or non-polymerizable groups. R is preferablyindependently selected from (L)_(n)-OH, (L)_(n)-NH₂, or(L)_(n)-O—CO—C₂H₃, wherein L is a linking group such as alkylene,arylene, siloxy, an ether linkage, or combination of thereof, and n isan integer from 0 to 10, or 0 to 6.

The functionalized POSS compounds in structures (I)-(III) above may bedenoted by the general formulas T_(m) ^(R) where m is equal to 8, 10 or12. When m=8, a common name of the compound is octakis(N)silsesquioxane, where N is the name of the R group.

In some embodiments, the formulations used to make the inorganic fillerof the ion-conducting polymer 310 may include mixtures of T₈ ^(R) POSScompounds with different R groups, mixtures of T₁₀ ^(R) POSS compoundswith different R groups, and/or mixtures of T₁₂ ^(R) POSS compounds withdifferent R groups. In some embodiments, the compositions of the presentdisclosure may include mixtures of T₈ ^(R), T₁₀ ^(R) and T₁₂ ^(R) POSScompounds.

In some embodiments, suitable POSS compounds include the compounds ofstructural formula (III) above, with functional groups including atleast more than one polymerizable moiety. Suitable examples includefunctional groups that are polymerizable moieties such as, for example,methacrylate, acrylate, vinyl, and epoxy. Suitable polymerizable POSScompounds are available from Hybrid Plastics Co., Hattiesburg, Miss.

In some embodiments, the ion-conducting polymer 310 is a thin filmsurrounding the ion-conducting membrane 320. In some embodiments, theion-conducting polymer 310 has a lower conductivity than theion-conducting membrane 320, but if the ion-conducting polymer 310 issufficiently thin, the high conductance of the ion-conducting membrane320 is not significantly impacted by the lower conductance of theion-conducting polymer 310. Further, a thinner ion-conducting polymer310 reduces inter-particle interfacial resistance between theion-conducting ceramic particles 314 and an electrode. In oneembodiment, the ion-conducting polymer 310 includes two planar surfaces306, 308, which can provide good interfacial contact with an electrode,if in direct contact with the electrode.

In various embodiments, the solid-state electrolyte 300 may have aconductivity of at least 10⁻⁷ S/cm measured at room temperature, or atleast 10⁴ S/cm measured at room temperature.

FIG. 4 is a schematic illustration of an apparatus 400 that may be usedto make a solid-state electrolyte 422 suitable for use in, for example,an energy storage device such as a Li-ion battery. The apparatus 400includes a mold 418 to shape the solid-state electrolyte 422. The mold418 retains a pre-polymer mixture 419A, which may be polymerized to forman ion-conducting polymer 419B.

In some embodiments, the pre-polymer mixture 419A includes polymerizablecompounds, an Li-salt, a polymerization initiator, and an optional ionicliquid. The polymerizable compounds of the pre-polymer mixture 419A maybe chosen from monomers, oligomers or mixtures and combinations thereof,any of which can form linear polymers, branched polymers, crosslinkedpolymers, star polymers, block copolymers, and mixtures and combinationsthereof.

The polymerization of the compounds in the pre-polymer mixture 419A maybe performed under curing conditions when the pre-polymer mixture 419Acontacts the ion-conducting membrane 420. The curing conditions mayinclude one or more of ultraviolet (UV) or visible light, heat,microwaves, ultrasound, or the like. In some embodiments, thepolymerization could instead be performed, in-situ, with the pre-polymermixture 419A inside the article 400 by applying a stimulus, wherein thestimulus may include one or more of ultraviolet (UV) or visible light,heat, microwaves, ultrasound, or the like.

The polymerization results in a thin, pressure-deformable ion-conductingpolymer 419B surrounding the ion-conducting polymer 420, which includesion-conducting ceramic particles 414 retained by an insulating polymericbinder 412. The resulting construction forms a solid-state electrolyte422 with a desired shape for a particular application.

FIG. 5 is a flow diagram illustrating an example technique 500 that maybe used to make an energy storage device. Referring also to FIG. 4, thetechnique 500 includes a step 502 in which an ion-conducting membrane420 is dipped into a pre-polymer mixture 419A including polymerizablecompounds such as monomers, oligomers and mixtures and combinationsthereof, a Li-salt, a polymerization initiator, and an optional ionicliquid.

In step 504, the pre-polymer mixture 419A is then at least partiallypolymerized when it is on the ion-conducting membrane 420 by exposingthe pre-polymer mixture 419A to one or more of ultraviolet (UV) orvisible light, heat, microwaves, ultrasound, or the like. In someembodiments, the technique may include the use of a mold, as such, forexample, the apparatus 400 of FIG. 4, although a mold is not required.For example, the ion-conducting membrane 420 that has been wet by thepre-polymer mixture 419A may be polymerized free-standing, or may besandwiched between glass plates to ensure that the resulting solid-stateelectrolyte construction 422 is sufficiently thin for use in a desiredapplication.

In some embodiments, the technique 500 of FIG. 5 further includes a step506 of assembling the resulting free standing solid-electrolyte 422 withsolid electrodes to form an energy storage device as shown in FIG. 2. Insome embodiments, the solid electrodes may include an anode and acathode that are of different materials. For example, the anode may be alithium-intercalating graphitic, a lithium titanate (LTO), silicon, or ametallic lithium electrode, while the cathode may be LiCoO₂,LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ (NCA), LiMn₂O₄, lithium nickel manganesecobalt oxide, or LiFePO₄. In other embodiments, the solid electrolyte422 may be used for applications other than Li-ion batteries, such as,for example, metal-air batteries or metal sulfur batteries.

FIG. 6 is a flow diagram illustrating another example technique 600 thatmay be used to make an energy storage device. Referring also to FIG. 4,the technique 600 includes a step 602 in which an ion-conductingmembrane 420 is dipped into a pre-polymer mixture 419A, wherein thepre-polymer mixture 419A includes polymerizable compounds (monomersand/or oligomers), a Li-salt, a polymerization initiator, and anoptional ionic liquid. In step 604, the ion-conducting membrane 420,which is wet with the pre-polymer mixture 419A, is then placed inbetween two solid electrodes (cathode and anode) and polymerized in-situin step 606 by applying one or more of ultraviolet (UV) or visiblelight, heat, microwaves, ultrasound, or the like to form anion-conducting polymer 419B. The ion-conducting membrane 420, incombination with the ion-conducting polymer 419B, provides a solid-stateelectrolyte 422. In some embodiments, the solid electrodes may includean anode and a cathode that are of different materials. For example, theanode may be a lithium-intercalating graphitic, a lithium titanate(LTO), a silicon, or a metallic lithium electrode, while the cathode maybe LiCoO₂, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ (NCA), LiMn₂O₄, or LiFePO₄. Inother embodiments, the solid electrolyte 422 may be used forapplications other than Li-ion batteries, such as, for example,metal-air batteries or metal sulfur batteries.

Embodiments of the present disclosure will now be described withreference to the following non-limiting examples.

EXAMPLES Example 1: Fabrication of Ion-Conducting Membrane

Ion-conducting membranes were fabricated using the process described inU.S. Patent Application Publication No. 2015/0255767, which isincorporated herein by reference in its entirety. An ethanol solubleadhesive tape, with adhesive side facing up, was attached to a siliconwafer and used as a substrate. The substrate was annealed at 75° C. for5 minutes to ensure the surface was flat and free of wrinkles. Li-ionconducting glass ceramic particles(Li_(1.6)Al_(0.5)Ti_(0.95)Ta_(0.5)(PO₄)₃) were used as theion-conducting ceramic particles (from Ohara Corp., Rancho SantaMargarita, Calif.). The Li-ion conducting glass ceramic particles have aLi-conductivity of 7×10⁻⁴S/cm at room temperature and 1.1×10'S/cm at100° C. The Li-ion conducting glass ceramic particles within the sizerange of 45 μm to 63 μm were scattered on the adhesive tape. Thesubstrate was then shaken to distribute the unattached ion-conductingceramic particles to form a single layer, ion-conducting ceramicparticle film with a high packing density. A 10 wt % solution ofcyclo-olefin polymer (available under the trade designation Zeonor 1430from Zeon Corp., Japan) in decalin was coated on the ion-conductingceramic particles using a draw down coating application with a 20 μmgate opening.

To form a continuous polymer matrix around the particles, the solventwas largely removed by heating the coated ion-conducting ceramicparticles on the substrate at 70° C. for 3 hours. Then, the adhesivetape was removed by submerging the substrate into ethanol at 70° C.overnight, which resulted in the bottom part of the ion-conductingmembrane being exposed. The excess polymer on the top surfaces of theion-conducting ceramic particles was removed by etching in a dryreactive oxygen plasma (MARCH).

FIGS. 7A-7B show top-down and cross-sectional SEM images of theresulting ion-conducting membrane. Under those conditions after etching,the insulating polymeric binder only filled in between theion-conducting ceramic particles, and both top and bottom parts of theion-conducting ceramic particles were not covered by the insulatingpolymeric binder.

Example 2: Preparation of Ion-Conducting Polymer Pre-Polymer MixtureIncluding Crosslinked PEG System

A pre-polymer mixture to form a crosslinked PEG ion-conducting polymerwas prepared by mixing a 4 to 1 molar ratio of poly(ethylene glycol)methyl ether acrylate (PEGMA, molecular weight=480) to polyethylene(glycol) diacrylate (PEGDA, molecular weight=700). Then, LiTFSI, as theLi-salt, was added with the molar ratio of EO/Li=20, wherein EO is arepeating number of ethylene oxide units in the PEGMA and PEGDA. A 60 wt% of ionic liquid (1-butyl-1 methylpyrrolidinium bis(triflouromthylsulfonyl)imide) was added to the total mass of PEDMA andPEGDA as a plasticizer. Finally, 1 wt % to the total mass of PEDMA andPEGDA of initiator (Darocur 1173 for UV curing and ARM for thermalcuring) was added to the system. The pre-polymer mixture preparation wasperformed inside a glove box at room temperature. The pre-polymermixture was stirred until a homogenous solution was obtained, generallyfor 7 to 8 hours.

Example 3: Characterization of Intrinsic Ionic Conductivity ofCrosslinked PEG Ion-Conducting Polymer

150 μL of the pre-polymer mixture prepared by the method shown inEXAMPLE 2 was sandwiched between two Teflon-coated quartz plates,separated by a spacer. The pre-polymer mixture was then polymerized bybeing exposed to 365-nm UV light for 90 s at 9 mW/cm².

The ion-conducting polymer obtained by this process showed a glasstransition temperature of −55° C. (by DSC), a thermal stability up to300° C. (by TGA), a storage modulus of 0.04 MPa at 25° C. (by DMA), andan ionic conductivity of −5×10⁻⁵ S/cm at room temperature and 7.6×10⁻⁴S/cm at 70° C. (by impedance analyzer).

Example 4: Integration of Crosslinked PEG Ion-Conducting Polymer withIon-Conducting Membrane

A composite solid-state electrolyte comprised of a crosslinked PEGion-conducting polymer and an ion-conducting membrane was prepared bywetting the ion-conducting membrane of EXAMPLE 1 with the PEGpre-polymer mixture of EXAMPLE 2. Then, the ion-conducting membrane wetwith the pre-polymer mixture was polymerized by radiation with 365 umUV-light for 90 sec to obtain the ion-conducting polymer.

FIG. 8 shows the cross-sectional SEM image of the resulting solid-stateelectrolyte with total thickness of about 90 μm. To minimize thethickness of PEG ion-conducting polymer layer, two quartz plates wereused to sandwich the ion-conducting membrane wet by the pre-polymermixture before UV polymerization.

Example 5: Preparation of Li—Li Symmetric Cell with PEG Ion-ConductingPolymer Coated on Ion-Conducting Membrane

To ensure good interfacial contact between the solid-state electrolyteand Li-electrodes, in-situ PEG polymerization was performed aftercoin-cell assembly with Li-electrodes. An ion-conducting membrane ofEXAMPLE 1 was immersed into the PEG pre-polymer mixture of EXAMPLE 2 inthe presence of an AIBN initator. The ion-conducting membrane, wet withthe pre-polymer mixture, was then placed in between two Li-foils toassemble a Li—Li symmetric coin cell energy storage device. The coincell was then heated at 70° C. for 24 hours in a vacuum oven to inducethermal crosslinking of the PEG pre-polymer mixture within the cell toform the ion-conducting polymer surrounding the ion-conducting membrane.

Example 6: Cycling Behavior of Li—Li Symmetric Cell with PEGIon-Conducting Polymer Coated on Ion-Conducting Membrane

To demonstrate the electrochemical performance of the solid-stateelectrolyte comprised of the PEG ion-conducting polymer andion-conducting membrane, the Li—Li symmetric coin cell prepared usingthe method of EXAMPLE 5 was cycled using a VMP3 BioLogic multi-channelpotentiostat. The cell was discharged and charged sequentially for 6hours each cycle at a current density of 0.2 mA/cm².

Referring to FIG. 9, the cell demonstrated a good plating and stripingprofile for more than 400 hours, which was more than 70 cycles.

Example 7: Preparation of Ion-Conducting Polymer Pre-Polymer MixtureIncluding Crosslinked POSS-PEG System

A pre-polymer mixture to form a crosslinked POSS-PEG ion-conductingpolymer was prepared by mixing a 10 to 1 mass ratio of poly(ethyleneglycol) methyl ether acrylate (PEGMA, molecular weight=480) with cagecompounds including methacryl polyhedral oligomeric silsesquioxane(POSS). This was followed by adding LiTFSi with the ratio of EO/Li=20and 1 wt % of initiator (Darocur 1173) to the total mass of PEGMA andPOSS. The pre-polymer mixture preparation was done inside a glove box atroom temperature. The pre-polymer mixture was stirred until a homogenoussolution was obtained, generally for 7 to 8 hours.

Example 8: Characterization of Intrinsic Ionic Conductivity ofCrosslinked POSS-PEG Ion-Conducting Polymer

150 μL of the pre-polymer mixture prepared by the method shown inEXAMPLE 7 was sandwiched between two Teflon-coated quartz platesseparated by a spacer. The pre-polymer mixture was then polymerized byexposure to a 365-nm UV light for 90 s at 9 mW/cm² to obtain theion-conducting polymer. The ion-conducting polymer obtained by thisprocess showed a glass transition temperature of −52° C. (by DSC), athermal stability up to 300° C. (by TGA), a storage modulus of 1.1 MPaat 25° C. (by DMA), and an ionic conductivity of about 4×10⁻⁵ S/cm atroom temperature (by impedance analyzer).

Example 9: Cycling Behavior of Li—Li Symmetric Cell with POSS-PEGIon-Conducting Polymer Coated on Ion-Conducting Membrane

To demonstrate the electrochemical performance of the solid-stateelectrolyte, a symmetric Li/Li cell was assembled with the solid-stateelectrolyte by following the process described in EXAMPLE 5, exceptusing the POSS-PEG pre-polymer mixture of EXAMPLE 7 instead of the PEGpre-polymer mixture of EXAMPLE 2 for the ion-conducting polymer. Thecell was discharged and charged sequentially for 6 hours each cycle at acurrent density of 0.2 mA/cm².

As seen in FIG. 10, the cell demonstrated very stable charge-dischargeprofiles without significant increase in the potential for more than 800hours, which was more than 130 cycles under the current density of 200μA/cm² at room temperature.

Comparative Example 1: Electrochemical Behavior of Li—Li Symmetric CellPrepared with Crosslinked PEG Ion-Conducting Polymer withoutIon-Conducting Membrane

For comparison, a crosslinked PEG ion-conducting polymer without anintegrated ion-conducting membrane was used as a solid-stateelectrolyte. A Li/Li symmetric cell was assembled by drop-casting oneLi-electrode with a PEG pre-polymer mixture prepared with the methoddescribed in EXAMPLE 2. Then, it was polymerized by exposure to a 365-nmUV light for 90 seconds. The crosslinked PEG-coated Li-electrode wasthen covered with another Li-electrode.

FIG. 11 shows the galvanostatic cycling behavior of the Li/Li symmetriccell assembled with the crosslinked PEG ion-conducting polymerelectrolyte. The cell was charged and discharged sequentially for aperiod of 10 hours at various current densities. As seen in FIG. 11, thecell had a short-circuit after a few cycles under a very low currentdensity of about 25 μA/cm².

Comparative Example 2: Electrochemical Behavior of Li—Li Symmetric CellPrepared with Crosslinked POSS-PEG Ion-Conducting Polymer withoutIon-Conducting Membrane

For comparison, a crosslinked POSS-PEG ion-conducting polymer without anintegrated ion-conducting membrane was used as a solid-stateelectrolyte. A Li/Li symmetric cell was assembled by drop-casting oneLi-electrode with a POSS-PEG pre-polymer mixture prepared with themethod described in EXAMPLE 7. Then, it was polymerized by exposure to a365-nm UV light for 90 s. The crosslinked POSS-PEG-coated Li-electrodewas then covered with another Li-electrode.

FIG. 12 shows the galvanostatic cycling behavior of the Li/Li symmetriccell assembled with the crosslinked POSS-PEG ion-conducting polymerelectrolyte. The cell was charged and discharged sequentially for aperiod of 6 hours each at various current densities. The cell showedimproved cycling performance (more than 200 cycles) compared to thecrosslinked PEG film electrolyte of COMPARATIVE EXAMPLE 1 under the lowcurrent density of about 25 μA/cm² due to the enhanced storage modulus(1.1 MPa for crosslinked POSS-PEG vs 0.04 MPa for crosslinked PEG).However, as shown in FIG. 12, the cell had a short circuit after a fewcycles under a current density of 100 μA/cm², and failed to functionproperly under a current density of 200 um/cm².

The solid-state electrolyte with the crosslinked POSS-PEG ion-conductingpolymer and ion-conducting membrane of the present disclosuredemonstrated good electrochemical plating-striping performance at theseelevated current densities.

Various examples have been described. These and other examples arewithin the scope of the following claims.

We claim:
 1. A method for making an energy storage device, the methodcomprising: dipping an ion-conducting membrane into a pre-polymermixture of an ion-conducting polymer, wherein the pre-polymer mixturecomprises polymerizable compounds, a compound that releases Li-ions, apolymerization initiator, and an optional ionic liquid; polymerizing thepre-polymer mixture under curing conditions when it is on theion-conducting membrane to form an ion-conducting polymer; andassembling a resulting free-standing solid electrolyte with electrodesto form an energy storage device.
 2. The method of claim 1, wherein thepolymerizable compounds are selected from monomers, oligomers, andmixtures and combinations thereof.
 3. The method of claim 1, wherein thepolymerizable compounds are selected from the group consisting ofmonomers that form linear polymers, monomers that form branchedpolymers, monomers that form crosslinked polymers, monomers that formstar polymers, monomers that form block copolymers, and mixtures andcombinations thereof.
 4. The method of claim 1, wherein thepolymerizable compounds comprise a polyethylene glycol.
 5. The method ofclaim 4, wherein the polyethylene glycol is crosslinked.
 6. The methodof claim 4, wherein the polyethylene glycol comprises an acrylate and/ora diacrylate.
 7. The method of claim 1, wherein the pre-polymer mixturefurther comprises an inorganic filler.
 8. The method of claim 7, whereinthe inorganic filler is selected from the group consisting of carbonnanotubes, silica nanoparticles, POSS compounds, metal oxides, andcombinations thereof.
 9. The method of claim 7, wherein the inorganicfiller comprises a POSS compound.
 10. The method of claim 1, wherein theion-conducting membrane comprises a contiguous solid structure of fusedand/or sintered ion-conducting ceramic particles.
 11. The method ofclaim 10, wherein the ion-conducting membrane has a first surface and asecond surface, wherein at least a portion of the ion-conducting ceramicparticles extend from the first surface to the second surface of theion-conducting membrane.
 12. The method of claim 10, wherein theion-conducting ceramic particles are retained in insulating polymericbinder.
 13. The method of claim 12, wherein the ion-conducting ceramicparticles have a top part and a bottom part that are not covered by theinsulating polymeric binder.
 14. The method of claim 10, wherein theion-conducting ceramic particles have an elastic modulus greater than 6GPa.
 15. The method of claim 10, wherein the ion-conducting ceramicparticles are selected from the group consisting of LiPON, LISICON(Li₁₄Zn(GeO₄)₄), LAGP (Li_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃), LATP(Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃), LATTP(Li_(1.6)Al_(0.5)Ti_(0.95)Ta_(0.5)(PO₄)₃), LLZO (Li₇La₃Zr₂O₁₂),Li-β-alumina, doped Li₃N, Li₂S—SiS₂—Li₃PO₄, Li₇P₃S₁₁, Li₁₀GeP₂S₁₂, andmixtures and combinations thereof.
 16. The method of claim 1, whereinthe compound that releases Li-ions is a Li-salt.
 17. The method of claim16, wherein the Li-salt is selected from the group consisting of lithiumhexafluoroarsenate (LiAsF₆), lithium perchlorate (LiClO₄ ⁻), lithiumhexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), lithiumtrifluoromethanesulfonate (LiCF₃SO₃), lithium nitrate, and lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI).
 18. The method of claim 1,wherein the curing conditions are selected from the group consisting ofultraviolet light, visible light, heat, microwaves, ultrasound, andcombinations thereof.